This invention is about Ceramic Metal Halide lamps (CMH) and the sealing technology of such lamps.
Often times one of the components in the electrode feedthrough of such lamps is made of a cermet material. Cermets have been known for a long time to provide acceptable solutions for the sealing of electrical feedthroughs to surrounding nonconductive materials. For example cermet materials have been made as early as 1979 by mixing course refractory oxide granules with fine metallic powders, such as tungsten, nickel and molybdenum to obtain electrical conductivity and yet a thermal expansion coefficients compatible with ceramic materials.
In later years, up to the early 1990's, the details of making the cermets with various particle size materials, their construction forms and their initial use in ceramic metal halide lamps were described by various lamp developers, but did not yet result in a practical ceramic metal halide lamp. Later on in the mid 1990's the first commercially viable CMH lamp was introduced and the whole field of metal halide lamps got a big boost as a result since the color characteristics, the kind of chemistries that one could use and the efficacies obtained were far superior to the quartz metal halide technology. While the initial lamps introduced had an electrode construction made out of Nb, Mo and W metals later CMH lamp introductions used cermets quite frequently. Much of the work attempted to either shorten the overall size of the extended plug construction, lower the cost of the materials used, increase reliability of the seal under high temperature conditions or provide an alternative seal that may be more manufacturable or some combination of these. In many of the cermet constructions the brittleness of the cermet is still an issue and needs to be solved.